The present invention relates to a technology for producing semiconductor devices and, particularly, to a semiconductor device equipped with a resin-sealed package of surface mount type, such as the one which has many pins and a small heat resistance, and is small in size and is produced at a decreased cost.
As ICs are now produced having many functions being highly densely fabricated and operating at high speeds, it has been desired to develop a surface mount resin-sealed package having many lead pins having a good heat-emitting property or a small heat resistance. A surface mount type resin-sealed package which is constituted as described below has been proposed in, for example, Japanese Patent Laid-Open No. 286558/1991.
In such a package, the tabs to which a semiconductor pellet is bonded and heat-radiating fin leads are integrally formed together, and the heat-radiating fin leads and heat-radiating fins outwardly protruding from a sealing resin member of the package are integrally formed together. Moreover, a heat sink is buried in the package on the side of the back surface of the tabs, and is mechanically coupled to the heat-radiating fin leads inside the package.
A QFP (quad flat package) which has a good heat-radiating property and whose outer leads are prevented from deforming has been disclosed in Japanese Patent Laid-Open No. 218262/1993.
This QFP employs a lead frame and in which tabs to which a semiconductor pellet is bonded and heat-radiating fin leads are formed integrally together, and the heat-radiating fin leads and heat-radiating fins outwardly protruding from the sealing resin member of the package are integrally formed together, the tips of the heat-radiating fins being outwardly protruded beyond the tips of the outer leads.
In the former device in which the heat sink and the heat-radiating fin leads are mechanically coupled together inside the sealing resin, however, the coupling portions impose limitation upon the arrangement of leads and upon the number of pins. Besides, the pellet must be bonded, wires must be bonded and sealing with resin must be executed after a plurality of heat sinks are coupled to a series of lead frames, deteriorating the throughput of production.
In the latter device in which the leads and the heat-radiating fins are constituted by a lead frame, a problem arouses that it is impossible to design a package, taking a sufficiently high heat-radiating performance into consideration.
The object of the present invention is to provide a semiconductor device whose outer leads can be prevented from being deformed yet maintaining a high heat-radiating performance.
Another object of the present invention is to provide a method of producing semiconductor devices at a low cost.
The above and other objects as well as novel features of the present invention will become obvious from the description of the specification and the accompanying drawings.
Among the inventions disclosed in this application, representative will be briefly described below.
That is, the semiconductor device has a feature that the semiconductor pellet is bonded to a main surface of the heat sink which is partly buried in a sealing resin member of a square shape, and the heat sink has a plurality of bumpers formed integrally therewith, the bumpers protruding from the corners of the sealing resin member and having tips which are arranged on the outer sides of the row of tips of the outer leads which are led out from the four sides of the sealing resin member.
A method of producing semiconductor devises comprises:
a step of preparing a series of lead frames having unit lead frames which are arranged in a row and in each of which the outer leads and inner leads are radially arranged from the region where a semiconductor pellet is provided;
a step of preparing a series of heat sinks having unit heat sinks which are arranged in a row, and having main surfaces to which the semiconductor pellets are to be bonded and a plurality of bumpers that are integrally formed together therewith;
a step of coupling the series of lead frames and the series of heat sinks together outside at least a pair of bumpers of the unit heat sinks;
a step of bonding the semiconductor pellets onto main surfaces of the unit heat sinks;
a step for electrically connecting the electrodes of the semiconductor pellets to the inner leads with bonding wires thereto;
a step of sealing the semiconductor pellets, inner leads, and at least the main surfaces of the unit heat sinks on the semiconductor pellet side with a resin;
a step of cutting the series of lead frames to form the unit lead frames; and
a step of cutting off the unit heat sinks from the series of heat sinks.
According to the above-mentioned semiconductor device, the heat generated by the semiconductor pellet is conducted to the heat sink; i.e., the semiconductor pellet is cooled quite efficiently.
Moreover, since the tips of bumpers arranged at the corners of the sealing resin member protrude outwardly beyond the tips of the outer leads, in case an external force is unexpectedly given to the package during the steps of production, during the shipment to the user, or while it is being mounted by the user, the bumpers absorb the external force, preventing the outer leads from being deformed.
According to the above-mentioned method of producing semiconductor devices in which the coupling portion between the heat sink and the lead frame is not buried in the sealing resin member, no limitation is put on the layout of the inner leads by the coupling portion in the sealing resin member. Besides, an increase in the degree of freedom of laying out the wirings permits the bumpers to be arranged, making it possible to produce even semiconductor devices that do not have leads for the heat-radiating fins.
Since the heat sink is coupled to the lead frame, furthermore, the devices for fabricating the semiconductor pellets and inner leads of the prior art may be employed. Before being coupled, furthermore, the heat sink is separate from the lead frame. Therefore, the thickness of only the heat sink can be easily increased, contributing to further enhancing the heat-radiating performance with ease.